Unlock the Power of Maps in Java
What is a Map in Java?
Imagine having a collection of data where each element is associated with a unique identifier, known as a key. This is essentially what a Map in Java is – a data structure that stores elements in key-value pairs. The keys are unique, and each key is linked to a single value. Think of it like a phonebook, where names (keys) are associated with phone numbers (values).
How Maps Work
In the diagram below, we have three countries – United States, Brazil, and Spain – represented by their corresponding keys: us, br, and es. We can access these values using their respective keys.
Key Features of Maps
The Map interface maintains three distinct sets:
- The set of keys
- The set of values
- The set of key-value associations (mapping)
This allows us to access keys, values, and associations individually.
Classes that Implement Map
Since Map is an interface, we can’t create objects from it directly. Instead, we use classes that implement the Map interface, such as:
- HashMap
- EnumMap
- LinkedHashMap
- WeakHashMap
- TreeMap
These classes are defined in the collections framework and implement the Map interface.
Interfaces that Extend Map
The Map interface is also extended by subinterfaces, including:
- SortedMap
- NavigableMap
- ConcurrentMap
Getting Started with Maps
To use Maps in Java, we need to import the java.util.Map package. Once imported, we can create a map using classes like HashMap.
Methods of Map
The Map interface includes a range of useful methods, including:
- put(K, V): Inserts a key-value association into the map
- putAll(): Inserts all entries from a specified map into this map
- putIfAbsent(K, V): Inserts an association if the key is not already associated with a value
- get(K): Returns the value associated with a specified key
- getOrDefault(K, defaultValue): Returns the value associated with a key, or a default value if the key is not found
- containsKey(K): Checks if a specified key is present in the map
- containsValue(V): Checks if a specified value is present in the map
- replace(K, V): Replaces the value of a key with a new specified value
- remove(K): Removes an entry from the map represented by a key
Implementation of the Map Interface
Let’s explore how to implement the Map interface using classes like HashMap and TreeMap.